The overall objective of this project is to develop a tissue equivalent immobilization device (TEID) for various radiologic procedures. The initial impact of this project will be in the area of Digital Subtraction Angiographic (DSA) runoff studies allowing for the first time, precise image re-registration for time-mode subtraction of images acquired before and after injection of contrast media into a patient's vascular system. Advantages of utilizing TEID include: increased patient comfort, utilization of the full dynamic range of the imaging chain, increased digitization accuracy, assured immobilization and ease of equipment handling. The stated objective will be achieved through systematic development of engineering design specifications, prototype construction, and evaluation utilizing an existing prototype DSA system with computer controlled table top movements for runoff studies. Phase II will entail modification of the initial design per specifications derived from Phase I, development of an ideal attenuating medium, adaptation of TEID for therapeutic radiologic procedures, production and advanced placement of TEID in service.